Nonaqueous-electrolyte batteries and nonaqueous electrolytic solutions

a technology of electrolytic solutions and nonaqueous electrolysis, which is applied in the direction of positive electrodes, cell components, electrochemical generators, etc., can solve the problems of reducing battery safety, low thermal stability, and a substance in a charged state, and achieves high initial output, high discharge capacity, and high capacity retention

Inactive Publication Date: 2012-09-27
MITSUBISHI CHEM CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0030]According to the nonaqueous-electrolyte batteries of the invention, an improvement in high-rate discharge capacity and an increase in output are attained in the case where a lithium-containing metal oxide having an olivine structure is used as a positive-electrode active material, by incorporating a chain ether into a nonaqueous electrolytic solution and thereby lowering the viscosity of the nonaqueous electrolytic solution and improving the ionic conductivity thereof. Furthermore, by incorporating, in a specific proportion, a compound having the function of forming a negative-electrode coating film, the resistance of the coating film on the surface of the negative electrode is prevented from increasing excessively, while maintaining thermal and chemical durability. As a result, not only high high-temperature storability and cycle characteristics can be imparted, but also an improvement in high-rate characteristics and an increase in output can be attained in the battery which has undergone a durability test.
[0031]Moreover, by incorporating, in a specific proportion, a compound having the function of protecting the positive electrode, metal dissolution from the positive-electrode active material is inhibited and the resistance of the coating film on the surface of the positive electrode is prevented from increasing excessively, while maintaining thermal and chemical durability. As a result, not only high high-temperature storability and cycle characteristics can be imparted, but also an improvement in high-rate characteristics and an increase in output can be attained in the battery which has undergone a durability test.MODES FOR CARRYING OUT THE INVENTION
[0032]Embodiments of the invention will be explained below. However, the invention should not be construed as being limited to the following embodiments, and can be modified at will.
[0034]The nonaqueous electrolytic solution for use in the first aspect of the invention contains(1) a chain ether and(2) a cyclic carbonate having an unsaturated bond.
[0035]The nonaqueous electrolytic solution for use in the second aspect of the invention contains(1) a chain ether and(2) at least one compound selected from lithium fluorophosphates, lithium sulfonates, imide lithium salts, sulfonic acid esters, and sulfurous acid esters.
[0037]The chain ether preferably is a compound represented by the general formula R1OR2. In the formula, R1 and R2 each represent a monovalent organic group which has 1-8 carbon atoms and may have a fluorine atom, and R1 and R2 may be the same or different.

Problems solved by technology

Lithium cobalt oxide (LiCoO2), which is used as a positive-electrode active material as shown above, has a drawback that this substance in a charged state has low thermal stability and reduces battery safety.
Furthermore, nonaqueous-electrolyte batteries employing LiFePO4 as a positive-electrode active material have had the following problem.
When these batteries are repeatedly charged and discharged in a high-temperature environment of, for example, about 60° C., elements including iron which are contained in the active material partly dissolve away with repetitions of charge / discharge, and the dissolved iron adversely affects the negative-electrode active material constituted of a carbon material, etc.
As a result, the negative electrode itself is impaired in charge / discharge reversibility and other properties and is hence reduced in reactivity, and this tends to result in a decrease in the capacity or output of the nonaqueous-electrolyte batteries.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

Production of Negative Electrode

[0321]To 98 parts by weight of artificial-graphite powder KS-44 (trade name; manufactured by Timcal) were added 100 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (concentration of sodium carboxymethyl cellulose, 1% by mass) as a thickener and 2 parts by weight of an aqueous dispersion of a styrene / butadiene rubber (concentration of styrene / butadiene rubber, 50% by mass) as a binder. The ingredients were mixed together by means of a disperser to obtain a slurry. The slurry obtained was applied to one surface of a copper foil having a thickness of 10 μm and dried. This coated foil was rolled with a pressing machine to a thickness of 75 μm, and a piece of a shape having an active-material layer size with a width of 30 mm and a length of 40 mm and having an uncoated area with a width of 5 mm and a length of 9 mm was cut out of the rolled sheet. Thus, a negative electrode was obtained.

[Production of Positive Electrode]

[0322]Nin...

example 2

[0331]A sheet-form lithium secondary battery was produced and evaluated in the same manners as in Example 1, except that an electrolytic solution was obtained in a dry argon atmosphere by mixing 99.5% by mass mixture of ethylene carbonate (EC), dimethoxyethane (DME), and ethyl methyl carbonate (EMC) (volume ratio, 2:3:5) with 0.5% by mass vinylene carbonate (VC) and then dissolving sufficiently dried LiPF6 in the resultant mixture so as to result in a proportion thereof of 1.1 mol / L. The components of the electrolytic solution and the results of the evaluation are shown in Table 1 to Table 3.

example 3

[0332]A sheet-form lithium secondary battery was produced and evaluated in the same manners as in Example 1, except that an electrolytic solution was obtained in a dry argon atmosphere by mixing 99.5% by mass mixture of ethylene carbonate (EC), dimethoxyethane (DME), and ethyl methyl carbonate (EMC) (volume ratio, 2:3:5) with 0.5% by mass lithium difluorophosphate (LiPO2F2) and then dissolving sufficiently dried LiPF6 in the resultant mixture so as to result in a proportion thereof of 1.1 mol / L. The components of the electrolytic solution and the results of the evaluation are shown in Table 1 to Table 3.

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Abstract

The invention is to provide a nonaqueous-electrolyte battery which comprises a current collector, a positive electrode containing a lithium-containing phosphoric acid compound represented by LixMPO4 as a positive-electrode active material, a negative electrode containing a negative-electrode active material capable of occluding and releasing lithium ions, and a nonaqueous electrolytic solution containing a chain ether and a cyclic carbonate having an unsaturated bond.

Description

TECHNICAL FIELD[0001]The present invention relates to nonaqueous-electrolyte batteries. More particularly, the invention relates to nonaqueous-electrolyte batteries which employ nonaqueous electrolytic solutions that bring about excellent high-output characteristics and excellent durability when iron lithium phosphate is used as the positive electrode.BACKGROUND ART[0002]Nonaqueous-electrolyte batteries including lithium secondary batteries are being put to practical use in extensive applications ranging from power sources for appliances for so-called public use, such as portable telephones and notebook type personal computers, to vehicle-mounted power sources for driving motor vehicles or the like. However, nonaqueous-electrolyte batteries are increasingly required to have higher performance in recent years, and are required to attain battery characteristics, such as, for example, high capacity, high output, high-temperature storability, cycle characteristics, and high safety, on a...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): H01M10/0564H01M10/056H01M10/0525H01M10/0567H01M10/0568H01M10/0569
CPCH01M4/5825H01M10/0525H01M10/0569Y02E60/122H01M10/0564H01M2300/0037H01M10/0568H01M4/587H01M10/0567Y02E60/10H01M4/58H01M10/052H01M2004/028H01M2004/027
Inventor TOKUDA, HIROYUKI
Owner MITSUBISHI CHEM CORP
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